Preparation of tetraalkylallenes



United States Patent New .iersey No Drawing. Filed May 11, 1962, Ser. No. 194,168 6 Ciaims. (Cl. 260-681) This invention relates to preparation of tetraalkylallenes. Specifically, it is a process for producing tetraalkylallenes by pyrolysis of 2,2,4,4-tetraalkyl-3-hydroxy-3- butenoic acid B-lactones.

The principal object of this invention is to provide a novel method for production of tetraalkylallenes from available starting compounds by a simple and economical method that produces high conversion and yield. Other objects and advatages will appear from the following detailed description.

Tetrarnethylallene was described by B. K. Merezhkevskii, 1. Russ, Phys. Chem. Soc. 45, p. 1940 (1913), Zentra, 1914, vol, I, pp. 18141815. The method described there is impractical and expensive.

I have discovered a very simple method for preparation of tetraalkylallenes by pyrolysis of 2,2,4,4-tetraall yl- 3-hydroxy-3-butenoic acid fi-lactones. The novel pyrolysis is as follows:

wherein the substituents R, are selected from the group consisting of alkyl groups, preferably of from 1 to 8 carbon atoms, and alkylene groups which, with the carbon atom to which they are attached, form a saturated carbocyclic ring of 5 to 6 carbon atoms. The term tetraalkylallene as used in this specification, is intended to include the alkylene as well as alky-l substituents, within the scope of the above formula.

It would be expected that pyrolysis of 2,2,4,4-tetraalkyl-3-hydroxy-3-butenoic acid ,B-lactones would yield the corresponding dialkyl ketenes. Instead, a substantially quantitive conversion to the tetraalky-lallenes was found to occur. The pyrolysis can be carried out in glass, quartz, or steel tubes with apparently no eifect by the material of the tube upon the course of the reaction.

ithout using any special type of pyrolysis tube, unusally high conversion and yield can be obtained.

The starting compounds, 2,2,4,4tetraalkyl-3-hydroxy- B-butenoic acid 8-lactones are relatively new compounds. One method for preparation of such compounds is described in my co-pending United States patent application Serial No. 108,738, filed May 9, 1961, now Patent No. 3,062,836.

In general, the process of my invention is carried out by passing a 2,2,4,4-tetraalkyl-3-hydroxy-3-butenoic acid B-lactone through a pyrolysis tube at a tempearture in the range from 150550 C. and collecting the tetraalkylallene that is formed.

As a starting compound any compound having the general formula shown in the equation above may be used. In the structural formula above, the number of carbon atoms in the alkyl radicals is limited to 8 carbon atoms, which includes the preferred compounds; however starting compounds having larger alkyl substituents can be used in the process of the invention.

The optimum temperature for pyrolysis generally will occur between 150 and 550 C., depending upon other reaction conditions, such as the contact time (the time that a given molecule of reactant takes to pass through the pyrolysis zone), the diameter of the pyrolysis tube,

3,l3i,234 Patented Apr. 28, 1964 "ice the size and shape of the packing in the tube, whether a diluent gas is used and whether the process is operated at atmospheric pressure or under vacuum. The process works quite well under vacuum and a higher yield is generally obtained under vacuum.

In the pyrolysis tube, no special packing is needed; in fact, an open tube is suitable. The pyrolysis tube may be constructed of heat-resistmt glass, such as Pyrex brand or Vycor brand glass, iron, stainless steel, quartz, and the like. With higher lactones, pyrolysis can be effected simply by refluxing at atmospheric pressure and distilling oi the tetraalkylallene.

Following are examples illustrating specific embodiments of the invention.

A 1-inch x 14-inch Vycor tube, filled with Vycor chips, was heated by an electric furnace to 450 C. while a slow stream of nitrogen was passed through the system. Over a period of 6 hours, 1200 grams (8.6 moles) of 2,2,4- trimethyl-3-hydroxy 3 pentenoic acid B-lactone was pumped into the tube. The pyrolysate was collected in a flask equipped with a Dry Ice condenser. The efiiuent gases contained carbon dioxide. The temperature in the pyrolysis tube was maintained at 450-460 C. by an automatic controller during the reaction. The pyrolysate was distilled through an 18-inch packed column to yield 776.3 grams (94 percent yield) of tetrarnethylallene, B.P. 87- 87.5 C. (21 1.4405). The calculated analysis (C, 87.5%; H, 12.5%) for C7H12 was found (C, 87.6%; H, 12.6%). The magnetic resonance spectrum for the product showed only one peak, indicating that all of the protons in the molecule were equivalent, as would be the case in tetramethylallene. The product was dimerized to 1,2- diisopropylidene-3,3,4,4-tetramethylcyclobutane, RP. 78 79 C. (6 mm.), n -1.4934. This dimer is especially suitable for use as a fuel for jet engines, having a high boiling point, high density and high energy value per pound.

Example II By the same method described in Example I, 168 grams (1 mole) of 2-ethyl-2,4-dimethyl-3-hydroxy-3-hexenoic acid ,B-lactone yielded 113 grams (91 percent yield) of 1,3-diethyl-1,3-dimethylallene, Bl. -139 C.

Example 111 By the same method described in Example I, 252 g. (1.0 mole) 2-butyl-2,4-diethyl-3-hydroxy-3-octenoic acid fi-lactone yielded 193 grams (93 percent yield) of 1,3- dibutyl-1,3-diethylallene, B.P. 104106 C. (7 mm.).

Tetraalkylallenes, prepared by the method of the invention, are useful intermediates in a number of organic syntheses.

In the above examples the contact time based on the fl-lactone feed was about two seconds. Depending upon the other process conditions, the optimum contact time usuflly is in the range from about 0.5 second to about 10 seconds. Optimum contact time will be toward the lower end of this range when operating at reduced pressures. Reduced pressure can be obtained by operating under partial vacuum or by using a diluent gas such as nitrogen to reduce the partial pressure of the reactant. Optimum pressures will range hom about 5 mm. Hg, or an equivalent partial pressure of the reactant in a diluent gas, up to about one atmosphere pressure. Yields are substantially reduced at higher pressures. At extremely high temperatures, above about 550 C., some undesirable isomerization and cracking will occur and the yield of tetraalkylallene consequently will be reduced.

The invention has been described with reference to certain preferred embodiments, but it Will be understood that variations and modifications can be made within the scope of the invention definedin the following claims.

I claim:

1. A method for producing a tetraalkylallene, said method comprising pyroiysing a 2,2,4,4-tetraalkyl-3-hydroxy-B-alkenoic acid ,B-lactone at a temperature in the range from 150-550 C., and collecting the tetraalkylallene that is formed.

2. A method for preparation of allene compounds comprising pyrolysing at a temperature in the range from 150-550 C. a compound having the general formula:

wherein the substituents, R, are selected from the group cc-nsistingo'f alkylgrou'ps of from 1 to 8 carbon atoms and alkylene groups which, with the carbon atom to which they are attached, form a saturated carbocyclic ring of 5 to 6 carbon atoms.

3. A method for production of tetramethylallene comprising pyrolysing at a temperature in the range from 150-550 C. 2,2,4-trimethyl-3-hydroxy-3-pentenoic acid p-lactone.

4. A method for production of 1,3-diethyl-1,3-dimeth- 4 ylallene comprising pyrolysing at a temperature from -550 C. of 2-ethy1-2,4-dimethyl-3-hydroxy-3-hexenoic acid ,B-lactone.

5. A method for production of 1,3-dihutyl-L3-diethylallene comprising pyrolysing at a temperature from 150 550 C. of 2-butyl-2,4-diethyl-3-hydr0Xy-3-octenoic acid B-lactone.

6. A method of producing allene compounds comprising heating, at a temperature from ISO-550 C. and at a contact time from 0.5 to 10 seconds and at a pressure from 5 to 760 mm. mercury, a compound having the general formula:

wherein the substituents, R, are selected from the group consisting of alkyl groups of from 1 to 8 carbon atoms and alkylene groups, which, with the carbon atom to which they are attached, form a saturated carbocyclic ring of 5 to 6 carbon atoms.

Referenccs Cited in the file of this patent UNITED STATES PATENTS 2,478,388 Hagemeyer Aug. 9, 1949 

1. A METHOD FOR PRODUCING A TETRAALKYLALLENE, SAID METHOD COMPRISING PYROLYSING A 2,2,4,4-TETRAALKYL-3-HYDROXY-3-ALKENOIC ACID B-LACTONE AT A TEMPERATURE IN THE RANGE FROM 150-550*C., AND COLLECTING THE TETRAALKYLALLENE THAT IS FORMED. 